Means for improving the electronic exposure of photographic emulsions



Man-ch 27, N45. J. WHITTAKER 2,372,465 MEANS FOR IMPROVING THE ELECTRONIC EXPOSURE OF PHOTOGRAPHIC EMULSIONS Filed March 25, 1942 Zmnentor Cittorneg Patented Mar. 27, 1945 S FBR IMPROVING" THE ELECTRONIC" PHOTOGRAPHIGL EMUIZ- J ames'L. Whittaker, Woodbury, N. J1, assignor to Radio Corporation of America, a corporation of'Delaware Application: March. 23, 1942,, Serial N 435, 78&

reclaims.

This invention relates: generally to. means. for: controlling. electron velocity and particularly tomethods of and: apparatus for controlling thevelocity and scattering; electrons in. electronic apparatus. for the; purpose. of obtaining optimumv electron velocity and. diffusion for the exposure of sensitized emulsions or forforming electronic images;

It has; been customary to. accelerate the elec-- trons irradiating theobject inan electron microscope1to. velocities: at. which. the. electrons pierce the object. Inmany instances suchvelocities-require accelerating voltages. in excessof: 100 kilo volts. Experiments indicate thatv such velocities; are inefficient for exposure of photographic emulsions since the. optimum velocity for this purpose is. produced. by accelerating; voltages of approxi'-- mately 80. to 100 kilovolts, depending. upon the emulsion characteristics. Velocities-substantially above. or below this critical valueproduceless eflect upon. photographic emulsions. and: therefore: require. longer exposure. for a given image density. Therefore, it is desirable toirradiate the. object. or otherwise. utilize the electron beam. at the most: advantageous.velocity'and: then alterthe. velocity to: the: optimum value for exposure of the sensitized emulsion.

The; apparatus described in this application is disclosed but not: specifically claimed in. the copending application of. Richard F. Baker, Serial;- No. 435,827., filed.March. 23,. 1942, and; assigned to: the; same. assignee.

An.objectofthisinventionisto provide-ameth 0d, of and means for changing thevelocity'of: an: electronbeam in. an electron microscope or other electronic device priortouthe.impingement of the electrons .on aphotographically sensitized emulsion'. Another object. is to provide. means for changing the velocity of. electrons to the-optimum valuerequired. for exposure. of a sensitized emulsionor: for forming electronic images, Anotherobject. is to providein anelectron microscope, or similar electronic device, a velocity controllingelectrode for altering the velocity of electrons im-- pinging: on the sensitized. emulsion. of a photographic target.

Another objectis toprovidea screen electrode having predetermined electron scattering char acteristics; An additional objectistoprovide se-- lective means for accelerating 'or' decelerating electrons to a predetermined value for the exposure of a sensitized emulsion ora fluorescent screen.

The invention will be described with reference to the; drawing of which-Figure 1 is a schematic diagram of. the: invention, andzFigure 2. iswa graph of: the. electron: sensitivity characteristics; of. a typical photographic: emulsion.

Referring to the drawing,.E.ig.. 1. is an electronic: device in which an electronbeam is caused; to. expose a photographic. emulsion... An: electron-.- source I issuppliediwitnpower from a. battery: or: any suitable. source 2. Electrons. emitted by the. source I are drawn'toward the acceleratingelectrode 3"which is=supplied:with a high positivepoatential from the battery. orrother-power source; 4. The accelerating. electrode. causes the electron. beam to:penetrate the object. or; specimen 5.. electrostatic: or a magnetic. electron. focusing. means 6 causes the electron. beam to berfocusedz upon the photographically sensitized surface. 1 oithebase-B; Since the velocity of the electrons 9 required for penetration: of the obiect. 5515 con-- siderablyhigher. than the optimum. electron ve:-. locityfor. exposure of. the photographic emulsion, theelectrode H1- is supplied with a negative potential,.from the. battery or other-source H through? the switch 12, to. reduce.- the electron velocity to the optimum exposure value in the vicinity 1.3 of the image upon thersensitized. emulsion surface:

The: electrode: ID- should preferably be. dish shape-in order that the emulsion. I andsupport 8 may be maintained. at substantially the. same:- negative: potentialras the electrode. IIowever,:any form which accomplishes desired. electron velocity control while maintaining the photographic me.-- diumat substantially; the: electrode potential, will. be; satisfactory. Theelectrodeiust: described will: decelerate; the. electrons without causing. undessired electron scattering or difiusion inherentv in other decelerating: means. Freedom from excessive electron scattering, is particularly important. when electron images of highdefinition are de-- sired;

If some degree" of: electron. scattering; is: found to. be. advantageous-in particular apparatus, this:

may: be; readily accomplished by the addition: of

thin metal. foil: or grid element Mr. connected; to,.

The electrodeto, either with or without thescattering electrode IA; maybe used foracceleratsing the electron image if the electron. velocity:

after penetration of. the object or specimen 5': is.

insufiicient for: satisfactory exposure. of: the photographic emulsion. Acceleration. may" be. obtained't'oa desireddegreeby connecting 'the elecs trode l0, and, if desired, the electrode M, to a suitable positive potential from the battery H, or other source of power, through the reversing switch I2.

Fig. 4 is a graph in which the curve S indicates the sensitivity of a typical photographic emulsion to electron velocities produced by acceleration voltages from zero to 300 kilovolts applied to the electrode 3 without no potential .applied to the electrodes 10 and M. It is apparent that the emulsion sensitivity commences at about 3 kilovolts and continues to rise to a maximum ,at approximately 80 kilovolts, after which it drops to a relatively low value as the accelerating voltage is increased. The optimum value of voltage varies somewhat with emulsion characteristics.

It will be seen that the means which have been described operate on an entirely different principle than typical optical filters, in that this invention controls the velocity and scattering of electrons impinging on a photographic emulsion While optical filters control either the frequency or the intensity of the light beam applied to the emulsion. Experiments indicate that the effect described is probably not due to secondary electronic emission in the velocity control element or to fluorescence or radiation from the velocity controlling element or the photographic emulsion. While no attempt has been made to explain the reasons for the relation between photographic emulsion sensitivity and electron velocity, experimental data clearly shows that the relation exists and that electron velocity can be controlled for optimum emulsion efiiciency by the apparatus dis closed as this invention.

I claim as my invention:

1. Electronic image apparatus including an electron beam, electron image focusing means, and an electron responsive photographic target, electron image velocity changing means in the path of said beam adjacent said target comprising an electrode substantially transparent to said electron image and a source of potential connected to said electrode to alter said image velocity to a predetermined optimum value.

2. Electronic image apparatus including an electron beam, electron image focusing means, and an electron responsive photographic target,

electron image decelerating means in the path of said beam adjacent said target comprising an open cylindrical electrode normal to said target, and a source of potential, negative with respect to said beam, connected to said electrode to alter said image velocity to a predetermined optimum value. 1

3. Electronic image apparatus including an electron beam, electron image focusing means,

and anelectron responsive photographic target,

source of potential connected to said electrode,

and additional electrode means adjacent said target for scattering the electrons of said beam.

5. In electronic apparatus including an electron beam and an electron responsive target, electron decelerating means in the path of said beam adjacent said target comprising an open cylindrical electrode normal to said target, and a source of potential negative with respect to said beam connected to said electrode and additional electrode means adjacent said target for scattering the electrons of said beam.

6. In electronic apparatus including an electron beam and an electron responsive target, electron accelerating means in the path of said beam adjacent said target comprising an open cylindrical electrode normal to said target, and a source of potential positive with respect to said beam connected to said electrode, and additional electrode means adjacent said target for scattering the electrons of said beam.

7. In electronic apparatus including an electron beam and an electron responsive target, electron velocity changing means in the path of said beam adjacent said target comprising an electrode substantially transparent to said beam and a source of potential connected to said electrode to alter the electron beam velocity to a predetermined value for the exposure of said target, and additional electrode means adjacent said target for scattering the electrons of said beam.

8. Electronic apparatus including an electron beam and an electron responsive photographic target, electron velocity changing means in the path of said beam adjacent said target comprising an electrode substantially transparent to said beam and a source of potential connected to said electrode to alter the electron beam velocity to a predetermined value for the exposure of said target.

9. Apparatus of the type described in claim 8 including electrode means adjacent said target for scattering the electrons of said beam.

10. Electronic apparatus including an electron beam and an electron responsive photographic target, electron decelerating means in the path of said beam adjacent said target comprising an open cylindrical electrode normal to said target, and a source of potential, negative with respect to said beam, connected to said electrode to alter the electron beam velocity to the optimum value for the exposure of said target.

11. Electronic apparatus including an electron beam and an electron responsive photographic target, electron accelerating means in the path of said beam adjacent said target comprising an open cylindrical electrode normal to said target, and a source of potential, positive with respect to said beam, connected to said electrode to alter the electron beam velocity to the optimum value of the exposure of said target.

12. Electronic apparatus including an electro beam and an electron responsive photographic target, electron velocity changing means in the path of said beam adjacent said target comprising an open cylindrical electrode, substantially transparent to said beam, and normal to said target, and a source of potential connected to said electrode.

r 13. In an electron image device including electron image focusing means, the method of controlling an electron image impinging upon an electron responsive photographic target comprising focusing said image upon said target and electrically controlling the velocity of said image intermediate said focusing means and said target to provide optimum electron velocity for photographic exposure of said target.

JAMES L, WI II' TAKER 

